The Nicholson Method of Determination of the Standard Rate Constant of a Quasireversible Redox Couple Employing Cyclic Voltammetry: Everything One Needs to Know!

For more than 50 years, the Nicholson method has been the predominant technique for the electrochemical kinetic analysis of quasireversible redox couples, primarily due to its simplicity in determining the standard rate constant (k0). This method necessitates only the peak potential separation (ΔEp) to derive the kinetic parameter, ψ, where the slope of the ψ versus (nπDoFν/RT)−1/2 plot directly reflects k0. There are two approaches to ascertain ψ: one can either use the ψ vs. ΔEp dataset or an empirical equation. Nonetheless, the existence of three distinct ψ vs ΔEp datasets and 12 empirical equations in the literature creates ambiguity regarding the optimal choice for kinetic analysis. Furthermore, there is a lack of comprehensive guidelines and best practices regarding the correct way of application of the Nicholson approach. Researchers often overlook the inherent limitations and drawbacks associated with the Nicholson method, ultimately resulting in a considerable volume of misinterpreted findings in the existing literature. This Perspective examines the theoretical foundations and constraints of Nicholson’s approach, assesses the validity of different proposed ψ vs. ΔEp datasets and empirical equations, and tackles several fundamental questions regarding the Nicholson approach. Moreover, this approach offers a fresh ψ vs. ΔEp dataset for each mV interval of ΔEp, thus obviating the need for empirical equations to determine ψ for a particular ΔEp value. The claims are further corroborated by the experimental evaluation of k0 for [Ru(NH3)6]3+/[Ru(NH3)6]2+, [Fe(CN)6]3–/[Fe(CN)6]4–, and Eu3+/Eu2+ redox couples.